1. Field of the Invention
The present invention relates generally to truck frames. More specifically, the present invention relates to a multi-piece siderail (often a three-piece siderail) suitable for use in frames for medium trucks, heavy trucks, trailers, and other transportation equipment.
2. Description of the Related Art
Traditionally, vehicle frames or truck frames are composed of two siderails interconnected by a plurality of cross members. (It will be understood that the term truck frame, as used herein, relates equally to other vehicles and equipment frames such as those used in trailers, etc.) The truck frame then forms a foundation to which all other components are directly or indirectly affixed. Thus, the truck frame must be suitably strong and sufficiently rigid to not only support a relatively large amount of weight, but it must also retain its integrity as severe forces and stresses are applied during use. It might therefore seem logical to form the siderails from relatively thick, wide, heavy gauge steel beams. However, this is simply undesirable in most modern truck frames. The use of unduly rigid and thick steel for siderails greatly and unacceptably increases both the cost and the weight of the completed frame.
For some time it has been known to form each siderail of a truck frame from two separate pieces of steel. That is, each siderail is composed of separate steel members that are appropriately coupled to each other. This is a standard practice for fabricating frames used on light duty trucks. Light duty trucks are those trucks that are generally used for individual/personal use such as pick-up trucks, sport utility vehicles, or minivans. Typically, with a two-piece siderail, the joint of the siderail is located near the front seat of the cab or its equivalent. Thus, the front section of the siderail is used to support the engine and at least a significant portion of the cab. The rear section of the siderail supports a portion of the cab and the remainder of the vehicle.
As is well understood, there is a distinction between light duty trucks as one class of vehicles and medium or heavy duty trucks as a second class of vehicles. Often products for these different classes are produced by different manufacturers, using different manufacturing techniques, and in vastly different volumes. Some medium and perhaps some heavy duty trucks have employed a two-piece siderail in constructing the truck frame. For example, a commercial delivery van may be classified as a medium duty vehicle and could be formed using a variation of the two-piece siderail. Oftentimes, with heavy trucks, such as tractor trailers, the siderail is formed from a single piece of relatively heavy gauge steel. This is due to the increased weight and towing/loading capacities required by such vehicles. Alternatively, reinforced siderails have been used where an additional layer of metal is provided at various points to provide the prescribed strength or stiffness. These siderails have been designed to accommodate the high stresses typically generated in the center portion. Thus, the front and rear portions of these siderails are typically over-designed (e.g. capable of carrying loads that will never be experienced.) Due to the commercial nature of these vehicles, the increased cost in using heavy gauge single beam siderails has been accepted. Often these rails are straight in sideview and of constant section, requiring a high vehicle profile for axle travel--this, too has been accepted.
Sometimes a "doubler" of either "C" or "L" shape is used to reinforce and stiffen the center siderail and a portion of the rear siderail--but this add-on piece is usually constrained to the height of the base siderail, not enjoying the greater weight efficiency of a deeper section.
In certain circumstances a "drop-belly" (one-piece) rail is used to achieve greater efficiency. This design includes a rail having a relatively deep (high) center portion and shallower end portions. Manufacturing such a rail requires expensive contoured tooling that is adjustable for each of the many specialized wheelbases typical of medium and heavy truck applications. Furthermore, this design lacks a desired overlap at the high stress rear spring front hanger. While this drop-belly rail is the most weight-efficient of past-practice siderails, it also has by far the highest tool and unit costs, considering the many tool set-ups for low-volume application. Additionally, this design creates scrap material in the shallower front and rear sections.
A major improvement in light duty truck frames has been the ability to produce multi-piece siderails. This concept, as used in light duty truck frames, is more fully described in U.S. Pat. No. 5,149,132 to Ruehl et al. issued on Sep. 22, 1992 and U.S. Pat. No. 5,308,115, also issued to Ruehl et al. on May 3, 1994. Both patents are hereby incorporated by reference. With this multi-piece siderail design, the rear section is subdivided into two components. Since the front most section of the siderail often supports substantially less weight than the middle section, and the front and rear sections must accommodate appropriate amounts of axle or suspension travel, the front end section can sometimes be fabricated from lighter gauge material and both end sections can also have a smaller cross-section than the center section. In this design, the strength and stiffness requirements for the center section is not compromised. Maintaining this stiffness insures that the ride quality of the vehicle is maintained at a desirable level. Furthermore, the highest local stresses often occur at the solid front attachment of the rear suspension which must react to braking and acceleration loads--a convenient spot to overlap center and rear siderail sections of this invention. Thus locally doubling stock at that load point, while using the spring hangers' fasteners to create the rail joint is an efficient rail configuration. Joining these three independent sections provides a way to form a single siderail that meets or exceeds structural integrity for the application better than the traditional one or two-piece design, while also potentially reducing both the cost and weight. Due to these potential cost, weight, quality and ride performance benefits provided by multi-piece considerations, multi-piece siderails have become an industry standard and represent a large percentage of the light duty truck frames being produced today.
Despite the potential cost and weight benefits provided by a multi-piece siderail, this design has not been used in medium and heavy trucks. The siderails utilized for these applications are usually much longer than those utilized in light duty trucks. Also due to the nature of the vehicle, the siderails will be required to support far greater weight. Hence, longer and more rigid siderails are required and frame designers have been reluctant to investigate the three-piece siderail. Rather, the industry has relied on one-piece and in some cases two-piece siderails constructed from heavy gauge material and/or reinforced siderails. This presents little opportunity to modify the design and weight characteristics of the vehicle's frame. This also limits any opportunity to generate manufacturing efficiencies which could be achieved using common components for various frames.
As mentioned, medium and heavy truck frames typically handle much heavier loads. Consequently, the frame itself must be much larger. In one aspect, the height of the frame becomes much taller in order to handle these weight loads. Along with this increase in height comes a potential for localized buckling or "oil-canning"(i.e. deflection of the web). Heavy gauge steel has historically been used to avoid this potential problem, thus eliminating one important benefit of the multi-piece siderail (i.e. potential weight reduction). This creates yet a further reason why three-piece siderails have not been used in the medium or heavy truck market.
As mentioned above, the markets for light duty trucks and medium/heavy duty trucks are quite different. In addition to the varying load requirements, the volume and product mix is drastically different. In the medium/heavy duty truck market, much lower volumes are involved, thus not providing as much potential for economies of scale. Additionally, multiple configurations are often desired by the vehicle manufacturers. Consequently, manufacturing costs can be very substantial due to this market characteristic. Obviously, truck frames manufactured with single piece siderails make it very difficult to achieve any economies of scale. Consequently, any potential reduction in manufacturing cost is of great benefit.
Therefore, there exists a need to provide a multi-piece siderail system suitable for use in medium and heavy duty trucks that will provide the required degree of rigidity and support while potentially reducing the overall cost and weight of the frame. Further, there exists a need to provide a siderail that can be efficiently manufactured, possibly using common components to create a variety of particular frame designs.